Suppress protobuf related Windows warnings

[mjcarroll]

🦟 Bug fix

Summary

Followup to gz-msgs#256: gazebosim/gz-msgs#256 (comment)

There were a few more warnings present, which come from "unprotected" protobuf includes. This takes every protobuf (library, not generated) include statement and wraps them with the correct pragmas.

Checklist

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[mjcarroll]

CC: @Blast545

[chapulina]

The UNIT_Discovery_TEST failure looks new

[mjcarroll]

The UNIT_Discovery_TEST failure looks new

It reliably fails on main for me as well.

[Blast545]

😢 The PR job seems to have more warnings that the reference buildfarm failure: (36 -> 55)
https://build.osrfoundation.org/job/ign_transport-pr-win/289/

[mjcarroll]

Using the SYSTEM include directive should cause MSVC to use the /external directive to mark those directories/includes to not show warnings.

In MSVC < 16.10, this requires an additional /experimental:external flag to be passed to the compiler: https://docs.microsoft.com/en-us/cpp/build/reference/external-external-headers-diagnostics?view=msvc-170

It looks like we are using something newer than that, so I'm not sure where the issue is at this point.

[codecov]

Codecov Report

Merging #334 (93bf268) into main (80f71eb) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 93bf268 differs from pull request most recent head 9efd4f1. Consider uploading reports for the commit 9efd4f1 to get more accurate results

@@           Coverage Diff           @@
##             main     #334   +/-   ##
=======================================
  Coverage   88.11%   88.11%           
=======================================
  Files          52       52           
  Lines        4848     4848           
=======================================
  Hits         4272     4272           
  Misses        576      576           

Impacted Files	Coverage Δ
include/gz/transport/RepHandler.hh	85.36% <ø> (ø)
include/gz/transport/ReqHandler.hh	80.58% <ø> (ø)
include/gz/transport/SubscriptionHandler.hh	84.90% <ø> (ø)
src/NetUtils.cc	71.96% <ø> (ø)
src/Node.cc	92.30% <ø> (ø)
src/NodeShared.cc	77.76% <ø> (ø)
src/NodeSharedPrivate.hh	100.00% <ø> (ø)
src/cmd/gz.cc	95.31% <ø> (ø)
src/Discovery.cc	75.00% <100.00%> (ø)

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